1. Field of the Invention
This invention relates to a novel process for producing 6,6'-dihydroxy-3,3,3',3'-tetramethyl-1,1'-spirobiindane. More specifically, it relates to a process for producing 6,6'-dihydroxy-3,3,3',3'-tetramethyl-1,1'-spirobiindane, which comprises heat-treating 2,2'-bis(4-hydroxyphenyl)propane in the presence of a superacid-type resin or a perfluoroalkanesulfonic acid.
2. Description of the Prior Art
6,6'-Dihydroxy-3,3,3',3'-tetramethyl-1,1'-spirobiindane is a very useful substance as a material for resins.
Known methods for the production of 6,6'-dihydroxy-3,3,3',3'-tetramethyl-1,1'-spirobiindane include, for example, treatment of 2,2-bis(4-hydroxyphenyl)propane in about two times its amount of sulfuric acid at 140.degree. C. for 6 hours (U.S. Pat. No. 3,271,465), treatment of 2,2-bis(4-hydroxyphenyl)propane in a large excess of hydrobromic acid under reflux for 7 hours (J. Chem. Soc., Part I, pages 415-418, 1962), and treatment of 2,2-bis(4-hydroxyphenyl)propane with concentrated hydrochloric acid in an autoclave at 100.degree. C. for 24 hours (U.S. Pat. No. 3,271,465).
The industrial practice of these methods is not rational because the yield is low, the use of a large amount of sulfuric acid or hydrobromic acid reduces the volume efficiency, an operation is required to treat the waste liquor and make it pollution-free, or equipment having corrosion resistnace is required.